Project Summary/Abstract Study Title: A Pilot/Supportive Study of RC-2 to be Used for the Treatment of Non- Resectable Grade II and III Mast Cell Tumors in Dogs That Have Not Received Previous Therapy Except Corticosteroids. Experimental Design: This is an exploratory study designed as a prospective, open label, single site, single arm, clinical field study. Objectives/Purpose of study: The purpose of this clinical trial is to determine the safety and efficacy of the drug, RC-2, in client owned canines with non-resectable Grade II and III Mast Cell Tumors that have not received previous therapy except corticosteroids. Dogs meeting the enrollment/eligibility criteria will be recruited from the cases presented to the Texas A&M Veterinary Oncology Service. The primary efficacy variable will be the time to tumor progression (TTP). Other variables recorded and reported include ORR (overall response rate- partial remission or better), the disease control rate (stable disease or better), and the duration of response (DOR). The secondary objective is to determine the tolerability of the drug over a 3-month period in all dogs by recording and reporting in a real time fashion any adverse events. Justification: Mast Cell Tumors are the most common malignant skin tumor of the dog representing over 20% of the dermal and epidermal masses diagnosed in veterinary medicine. High-grade tumors (Grade II and III) have metastatic rates ranging from 50-90%. Once these tumors spread, the prognosis is poor and most dogs will die of this disease. The median survival time for a dog with a grade III mast cell tumor with aggressive therapy is approximately 1 year, but is reduced to 4-6 months in face of metastasis. New therapeutic approaches, such as RC- 2, are desperately needed to improve upon current disease outcomes. Study Site: Texas A&M University, College of Veterinary Medicine, Small Animal Clinical Sciences Study Dogs: The study will allow a minimum of 15 client owned dogs to be enrolled with non- resectable Grade II and III Mast Cell Tumors that have not received previous therapy except corticosteroids. Dogs must meet all eligibility criteria and no exclusion criteria. Study Standards and Ethics: This study protocol will be reviewed by the Institutional Animal Care and Use Committee at TAMU. Absolute compliance with this committee and its suggestions will be met before, during and after the study is performed. Written informed client consent will be obtained from each enrolled dog's owner before the dog can be enrolled. The welfare, treatment and care of the study animals will be ensured by the veterinary staff at the TAMU CVM Small Animal Clinic. 1